Digital cameras typically have a lens system, a photo detector (typically a charged coupled device CCD), a microprocessor, a display device (typically a liquid crystal display), a storage device, an image processing device (typically an ASIC or a DSP) and other components. Typically most of these components generate heat when operating. Some components generate more heat than other components.
The photo detectors used in typical digital cameras are sensitive to temperature. One of these sensitivities for the photo detector is the generation of noise. The higher the temperature of the photo detector the more noise that is created by the photo detector. When the temperature gets higher than some threshold temperature, the image created by the digital camera becomes visibly degraded. Other components in the digital camera are also sensitive to temperature, for example the analog-to-digital (A-to-D) converters, the liquid crystal display (LCD), the microprocessor, and the lens system.
Because of these temperature sensitivities, digital cameras may be programmed to control the temperature inside the camera by shutting down components that generate heat. Two methods are currently used to decide when to shut down heat generating components. The first method measures the total time that the components have been running. After some preset time, the heat generating components are turned off. This method does not take into account the temperature of the environment in which the camera is being used. Digital cameras are used in a wide variety of temperature conditions ranging from very hot on a summer day to very cold on a winter's day. When the camera is being used on a cold winter day the heat generating components may be shut down well before the photo detector of the camera gets too hot. Another problem with this method is camera cycling. When the user shuts the camera off and then restarts the camera within a short time (camera cycling) the total time measured for a heat-generating component may be reset. When the camera cycling time is shorter than the preset time, the heat-generating component will never be shut off.
The second method measures the inside temperature of the digital camera with a thermal couple. When the temperature measured by the thermal couple reaches a threshold value the camera either shuts down or slows down some heat generating components or the camera warns the user. This method has three problems. The first problem is that a thermal couple costs money. The second problem is that the thermal couple takes up room inside the camera. The third problem is that distance or various other internal structures will typically thermally separate the thermal couple from the photo detector. Due to this thermal separation the thermal couple does not give an accurate reading of the temperature of the photo detector. The photo detector is one of the most thermal sensitive components in digital imaging systems so it is important to accurately determine the temperature of the photo detector.
There is a need for a digital imaging system that can accurately and inexpensively determine and control the temperature of the photo detector.